1. Field of the Invention
The present invention relates to a processing apparatus such as a heat treatment apparatus for a semiconductor wafer using a gas and, more particularly, to a processing apparatus comprising a gas controller unit in which a flow control device for controlling the flow rate of a gas is incorporated.
2. Description of the Related Art
In a factory in which semiconductor wafers are manufactured, a working area is generally divided into a clean room and a maintenance room, a wafer convey system and the like are installed in the clean room, and a gas supply system and an exhaust system in a heat treatment apparatus are installed in the maintenance room. When wafers are subjected to film formation processing or etching processing, highly dangerous gases having a combustion aiding property, combustibility, and toxicity are used. For this reason, gas bombs are installed outside the working area, and the gases are supplied from the gas bombs into the reaction tube of the processing apparatus through a gas piping in the maintenance room.
On the other hand, in recent semiconductor manufacturing equipment, the number of processes increases, and the processes are complicated. For this reason, an entire system has a tendency to be made compact, and a gas controller unit constituted by integrating instruments for controlling gas in a unit to obtain a compact gas supply system, facilitate maintenance, and obtain a general-purpose system is considered. In addition, the followings are also considered. That is, this gas controller unit is installed to be integrated with an exhaust unit adjacent to, e.g., a heat treatment furnace, and the gas control unit is arranged above the heat treatment furnace.
This gas controller unit has filters, pressure switches, mass-flow controllers (flow control devices), blocking valves, check valves, and openable valves which are integrated and stored in a casing. An air supply pipe and an exhaust pipe are connected to the casing to circulate, e.g., air, in the casing, thereby preventing leakage of a gas from the unit into the maintenance room. In addition, this gas controller unit has a complex three-dimensional structure having a plurality of piping systems to cope with various heat treatment processes.
The above mass-flow controller comprises a flow-rate detection sensor for detecting a gas flow rate, a gas flow adjustment mechanism, and a control mechanism for controlling the gas flow adjustment mechanism in accordance with a flow-rate detection signal from the flow-rate detection sensor. Since the mass-flow controller serves as the principal part of the gas controller unit, the mass-flow controller must be periodically subjected to inspection and maintenance more frequently than other machines.
However, in a conventional mass-flow controller, since gas supply pipes are directly connected to an inlet and an outlet for a gas, the degree of freedom of piping is low, and only a planar piping structure is obtained. For this reason, a reduction in size of the gas controller unit is limited, and the gas controller unit has a considerably large size. Therefore, when maintenance of controllers on a processing vessel side is considered, the gas controller unit must be installed at a position having a long distance from the processing vessel, and an area occupied by the entire processing apparatus increases.
In addition, electrical parts such as electrical contacts, integrated circuits, and connector portions are preset in the gas controller unit. For example, some pressure switch has an output function for a pressure signal and a switching function and this pressure switch has a signal output circuit, a microswitch, a relay, and the like. The mass-flow controller has a processing circuit for outputting a flow control signal in accordance with a flow-rate detection value. The blocking valve has a solenoid valve for supplying air used for a blocking operation. Therefore, when a combustible gas leaks from the connection portion between, e.g., the gas controller and a piping, the leakage gas is exhausted from an exhaust duct because air is circulated in the casing of the gas controller unit. However, an explosion area concentration may be partially formed. Under this circumstance, when sparks are produced from the contact of the pressure switch, the contact of the solenoid valve for controlling the air of the blocking valve, or a defective connection of the electrical circuit, a small explosion may occur in the worst case. In addition, even when no combustible gas leaks, when a gas such as an oxygen gas having a combustion aiding property leaks, firing may occur from sparks or an over-heated portion. When the small explosion or firing occurs in the gas controller unit, the piping may be broken, or the gas controllers may be damaged.